Oregano needs no introduction, it is one of the most commonly used herbs, popular in Italian and Mediterranean dishes.
It can be grown throughout most of North America but its hardiness varies from variety to variety.
Hardiness Zones - Some varieties are hardy as far North as zone 3 & 4. Most withstand a moderate freeze. In marginal areas, grow oregano as an annual or in containers that can overwinter indoors.
Sunlight -Oregano does best in full sun, but will tolerate partial shade. In hotter climates, particularly in the south and southwest partial shade is better.
Soil and Fertilizer - Soil pH of 6.5 to 7.0 and a well-drained soil, organically enriched soil is best. Don't over fertilize oregano, it does fine with very little help in that dept., assuming you've maintained a proper soil pH. A side dressing of bone meal or fish emulsion at early and mid season should suffice if applied in a timely fashion.
Pruning - Oregano generally spreads easily and under optimal conditions it also spreads rather quickly. In late spring, you'll want to cut it back to about a third of its size in order to force the plant to grow bushier, rather than spread out.
In zones 3 to 7, protect the plants with a thick layer mulch over the winter months. You can also bring them indoors in some instances or use a cold frame. In the early Spring prune out dead stems before the plants emerges from dormancy and starts new growth.
Insects - Occasionally aphids or spider mites are a pest in Oregano, but not frequently. Serious infestations are uncommon and are generally easily treated.
I recommend Neem based products that are very effective and eco-friendly, they are not harmful to people, pets or livestock. Once you've sprayed the plant, don't harvest any leaves for several days. And when you do, wash them well before using.
Pyrethins, are also organic pesticides that will also work just fine. In mild infestations horticultural oil should suffice.